Post on 06-Aug-2020
Bluff Stabilization Techniques
Using an Integrated Planting Approach
Traditional Approach
• Not the best approach for long term sustainability of the site.
Integrated Approach
• The integrated approach incorporates soil bioengineering techniques using a combination of woody and herbaceous plant materials in various forms
Soil Bioengineering
• Soil Bioengineering: The practice of utilizing plant materials alone in such a way as to perform a structural function of stabilization
• Biotechnical Stabilization: Utilizing a combination of plants, geotextile fabrics, and/or structural measures for stabilization.
Factors affecting bluff stabilization
• Surface Water - creates rill/gully erosion• Ground Water - creates slumping and
slope instability• Bay Water – wave energy creates toe
erosion
Surface Erosion Solutions
• Direct surface water away from the top of the bluff
• Intercept water to keep it from running over the top of the bluff
• Protect the surface to prevent erosion– Herbaceous vegetation– Bioengineering techniques
(Herbaceous/Woody)– Hard surfacing
Vegetative ConsiderationsPlanting Techniques
• Seeding vs vegetative material• Plant types
– Dormant unrooted– Bare root– Containerized
Native or naturalized materials?• Caution with invasive plants
– Polygonum– Crownvetch
Woody Plant Functions Soil Bioengineering Systems
• Root reinforcement - root tensile strength mechanically reinforces soil.
• Soil moisture depletion - remove excess soil water through evapotranspiration.
• Buttressing and Arching - anchored & embedded stems/roots counteract downslope shear forces.
• Flexible stems deflect erosive energy
Vegetation
Herbaceous planting/seeding to protect the surface of the soil quickly
• Well adapted materials for variety of bluff conditions – Shaded to sunny– Sandy to Clayey– Wet to droughty
Soil Bioengineering Systems “Keystone Species”
Species
Shrub willows (Salix spp.)
Rooting Success
70%-100%
Shrub dogwoods
(Cornus spp.)
30%-70%
Willow Whips• 3/8” to 5/8” in diameter• 4-8 ft. in length• Cut when dormant• Nursery grown; same
diameter/branching pattern
Soil Bioengineering Species Commercially Available Willows
• ‘Streamco’ purpleosier willow (Salix purpurea)• ‘Bankers’ dwarf willow (Salix cottetii)• ‘Greenbank’ sandbar willow (Salix exigua)• Pussy willow (Salix discolor)• Silky willow (Salix sericea)• Prairie willow (Salix humilis)• Bebb willow (Salix bebbiana)• Heart-leaved willow (Salix eriocephala)
• Black willow (Salix nigra)
Sandbar willow
Pussy Willow
Silky willow
Prairie Willow
Soil Bioengineering Species Commercially Available Shrubs
• ‘Ruby’ redosier dogwood (Cornus stolonifera)
• ‘Indigo’ silky dogwood (Cornus amomum)
• Gray dogwood (Cornus racemosa) (Does not root well from dormant cuttings)
‘Ruby’ redosier dogwood(Cornus serecia)
Developed because of it’sprolific layering ability.
Soil Bioengineering Species Limited rooting ability
• Buttonbush (Cephalanthus occidentalis)• Elderberry (Sambucus canadensis)*• Ninebark (Physocarpus opulifolia)*• Arrowwood, Blackhaw (Viburnum spp.)*• Groundsel (Baccharis halimifolia)• Indigobush (Amorpha fruticosa)
• * indicates shade tolerance
Soil Bioengineering
• Utilizes vegetation to provide some structural support to the slope.
• Examples– Fascines– Brushmattressing– Live Staking
Live stakes• 3/8”-1.5” diameter• 1-3 ft. length• Avoid “mushrooming”
tops• Approx. 75% of the length
shall be inserted in the soil
A “living” live stake
Brushmattress Cross Section
Brushmattress
Installation of brushmattress After one growing season
Brushmattress Installation
Other Plant Forms
• Unrooted cuttings• Bare Root• Tubelings• Container
Unrooted Cuttings• 1/4”-3/8” diameter• 8”-12” length• Perform better in moist
soils• May be planted through
erosion control fabric
Rooted (bare root) plants• field dug, bare root• 3/8” at root collar• Root gel (Terrasorb)
increases survival in higher, drier bank zones
• May be planted though erosion control fabric
Tubelings
Containerized Plants
Container Fascine
Soil Bioengineering Species Bare root/Containerized
• Alder species (Alnus spp.)*• Red/Black chokeberry (Aronia spp.)*• Gray dogwood (Cornus racemosa)*• Sweet pepperbush (Clethra alnifolia)*• Winterberry holly (Ilex verticillata)*• Spicebush (Lindera benzoin)*• Witch-hazel (Hamamelis virginiana)*• Highbush blueberry (Vaccinium corymbosum)*
Coastal Bluff Stabilization Full sun/Drought tolerant Species
• Bayberry (Myrica pensylvanica)
• Winged sumac (Rhus copallina)
• Sand cherry (Prunus depressa)
• Sweetfern (Comptonia peregrina)
• Indigobush (Amorpha fruticosa)
• Groundsel (Baccharis halimifolia)
• American beachgrass (Ammophila breveligulata)
• Coastal panicgrass (Panicum amarulum)
• Switchgrass (Panicum virgatum)
• Saltmeadow cordgrass (Spartina patens)
• Coastal little bluestem (Schizachyrium scoparium var. littorale)
Plant Materials Costs
Plant Form Approximate Cost Unrooted cuttings $0.45-$0.75
Live stakes (1-3 ft.) $1.00-$1.50 Willow whips (4’-8’) $1.00-$3.00 Tubelings $1.25-$1.75 Bare root ( 1-0) $1.00-$2.00 Container (1 gal) $ 3.00-$12.00
Erosion Control Fabrics on Bluffs
Planting Trial Red Point-Cecil County
Red Point-Cecil County
Dormant Shrub Willow Planting
Herbaceous Plantings of beachgrass/saltmeadow cordgrass
Filling
• Filling is generally not a good idea• Slope is typically too steep to hold
materials in place• Fill materials may cover existing
vegetation• Cutting is usually preferred as it is more
stable• Organic matter will rot down and retain
water
General Bluff Planting Alternatives
• Establish good herbaceous cover then incorporate containerized, bare root, or unrooted shrubs, but no trees
• Plant a few scattered “mother” plants of well adapted shrub species and allow for natural succession due to seed dispersal
• Use the “Vegetative Barriers” approach to slope protection. Plant beachgrass, saltmeadow cordgrass, and/or coastal panicgrass on a tight (6”-8”) spacing within a row. Plant 2-3 rows one foot apart
• Soil bioengineering techniques may be used where water may be piping out of the slope.